Previous reports of the Principal Investigator have established that protein restriction before and during pregnancy results in a deficiency of neonatal brain cell number and protein content per such cell of the offspring. These results have now been confirmed in other laboratories. The objectives of the present proposal are: 1. The study of whether normal neonatal brain cell number (brain DNA) can be produced in the offspring of mothers fed full chemically defined diets before and during pregnancy, i.e. whether the known components of the diet are indeed sufficient for normal prenatal brain cell proliferation. 2. The study of whether a deficiency in neonatal brain cell number and protein content per cell can be produced by a restriction in essential amino acids or even a single essential amino acid in the mother's diet before and during pregnancy. Such a study appears of importance in view of the fact that many readily available natural foods are deficient in one or more essential amino acids.